Prepulse inhibition (PPI) of the startle eyeblink occurs whenever a non-startling prepulse precedes a startling stimulus by about 800 Milliseconds (ms) or less. Under such conditions, the magnitude of the startling reflex is greatly reduced. Current explanation of this phenomenon suggests that the inhibition of the startling reflex is meant to protect the perceptual analysis of the prepulse. The purpose of this research project is to examine the validity of this explanation. Three experiments are proposed, the first two will directly test the validity of this explanation by examining the extent to which the processing of a prepulse is affected by a subsequent startling stimulus. The third experiment will examine whether the phenomenon holds across modalities. Together, this project should provide a better understanding of the functional significance of the prepulse inhibition and help explain why a large number of clinical populations, such as schizophrenics, hyperactive children, and aged adults, do not exhibit this inhibitory phenomenon.